In the practice of gynecology a need often arises to determine the size and shape of a uterine endometrial cavity, for example, in connection with the fitting of an intrauterine contraceptive device. The prior art has not provided a convenient instrument for determining the size and shape of an endometrial cavity.
In a typical wing sound of the prior art, laterally deployed wings are used, after the sound is inserted into the uterus, to sense the position of the inner ostium of the cervix, and thus determine by difference the distance between the inner ostium and the fundus. (See H. M. Hasson, "Differential Uterine Measurements Recorded in Vivo", Obstetrics and Gynecology, Vol. 43, No. 3, pp 400-412, March 1974). In order to determine the shape of the uterine cavity, in accordance with the prior art, it is necessary to fill the cavity with a radiopaque fluid, expose the patient to X-ray radiation, and produce a radiographic image of the cavity on film. This image does not provide accurate information because it is distorted in both magnification and shape by an amount which depends on the source object and image distances and on the orientation of the uterine cavity plane with respect to the plane of the X-ray film.
The U.S. Pat. No. 3,706,307 to Hasson discloses a gynecological instrument for use in measuring anatomical features of the cervical canal, isthmus and uterus, characterized by a shaft telescoped within a tube and connected to the distal end of the tube, with the tube being preferably formed of a pliable material and provided with spaced slits adjacent the free end thereof so that the relative retraction of the tube relative to the shaft forms laterally extending wings in the area of the slits. Numerical indicia are provided along the length of a body for the shaft. When the device is inserted through the cervical canal to the top of the uterus the entire depth of the cervical canal and endometrial cavity can be measured. When the tube is retracted relative to the shaft and then the entire assembly is retracted until the isthmus is located, the difference between the two dimensions may be measured, indicating the individual length of each of the cervical canal and the endometrial cavity. The wings 48a, 48b identify the position of the inner ostrium of the cervix (FIG. 6).
The Baker U.S. Pat. No. 3,630,190 discloses an intrauterine probe adapted to probe the cervical canal and uterus, at least one annular ridge 14 being provided for providing an indication of contact with the outer limit of the cervix. The U.S. Pat. No. 2,241,451 to Fist shows a gynecological instrument which has an expanding member for measuring body cavities, in particular a vaginal cavity, as distinguished from a uterine cavity. The U.S. Pat. No. 3,095,871 to Mann et al. is an example of a prior art radiological-balloon method of determining the shape of a uterine cavity. The United Kingdom Pat. No. 141 of 1894 discloses an instrument for determining the limits of a body cavity, particularly a uterine cavity which includes radially extending tracing fingers 25 (FIG. 1).
There is an important need for an instrument which is free of distortion errors such as those above described, particularly in relation to the fitting of intrauterine contraceptive devices, so that the contraceptive device selected for a patient will more nearly correspond to the size and shape of the uterine cavity in which it is placed. There is substantial evidence that proper fitting of an intrauterine device to a uterine cavity will greatly reduced incidence of undesirable side effects caused by improperly fitted intrauterine devices. (See Hugh J. David and John Lesinski, "Uterine Variables in IUD Design", Intrauterine Devices: Development, Evaluation, and Program Implementation, R. G. Wheeler, G. W. Duncan, J. Joseph Speidel, editors, pp 91-96, 1974; S. Tejuja and P. K. Malkani, "Clinical Significance of Correlation Between the Size of the Uterine Cavity and the IUDC", Am. J. Obstet. Gynec. 105:620-627, 1969; Ibraham Kamal, M. Ghoneim, M. Talaat, M. Abdalla, "Retention and Expulsion of Intrauterine Contraceptive Devices", presented at the Population Council, Third International Conference on Intrauterine Contraception, Dec. 12-14, 1974).